A tandem image-forming device having a plurality of image-carrying members juxtaposed in a single direction are well known in the art. Japanese Patent Application Publication No. 2004-145228 discloses a tandem image-forming device having four image-carrying members, and an optical scanning unit to scan a laser beam to each image-carrying member, The optical scanning unit is arranged parallel to a plane occupied by the four image-carrying members in order to minimize the device.
The optical scanning unit includes a set of reflecting mirrors for each image-carrying member. Generally, the distance between the image-carrying member and the nearest reflecting mirror of the corresponding set differs among all image-carrying members Consequently, the sensitivity for adjusting the reflecting mirrors is different from one another, making the operations for adjusting the reflecting mirrors more complex.
It is an object of the present invention to provide an image-forming device that facilitates the adjustment of a reflecting mirror in an optical scanning unit.